1. Field of the Invention
The present invention relates to an SOI (Silicon On Insulator) substrate having a backside roughened and, more specifically, to a method of fabricating an SOI substrate having a backside sandblasted.
2. Description of the Related Art
As a method of preparing an SOQ (Silicon On Quartz) substrate, an SOG (Silicon On Glass) substrate, or the like, the SOITEC (Smart Cut) process developed by the Silicon On Insulator Technologies or the SiGen process developed by the Silicon Genesis Corporation has been used.
The SOITEC process is a method of obtaining an SOI substrate. According to the SOITEC process, a silicon substrate (donor substrate) into which hydrogen ions have been implanted through its surface to be bonded, and an insulating substrate (handle substrate) such as a quartz substrate or a glass substrate are bonded together; and the thus-bonded substrates is heated at a temperature of 400° C. or higher (e.g., at 500° C.) to thermally peel off a silicon film at a region with a highest concentration of implanted hydrogen ions (e.g., Japanese Patent No. 3048201, and Auberton-Herve, A. J. et al., “Smart Cut Technology: Industrial Status of SOI Wafer Production and New Material Developments,” Electrochemical Society Proceedings, Vol. 99-3 (1999) pp. 93-106). This process is based on a mechanism in which high-density “air bubbles,” called “microcavities” and formed by hydrogen ion implantation, are grown by heating, and a silicon film is peeled off by taking advantage of this “air bubble growth.”
The SiGen process is a method of obtaining an SOI substrate. According to the SiGen process, plasma treatment is applied to both or either of a surface of a silicon substrate (donor substrate) into which hydrogen ions have been implanted through the surface to be bonded, and a surface of an insulating substrate (handle substrate) to be bonded such as that of a quartz substrate or a glass substrate; the two substrates are then bonded together with both or either of the surfaces being activated; heat treatment is applied to the two bonded substrates at a low temperature (e.g., at a temperature of 100 to 300° C.) to increase the bond strength of the two bonded substrates; and the silicon film is mechanically peeled off at ordinary temperature (e.g., U.S. Pat. Nos. 6,263,941, 6,513,564, and 6,582,999).
A main difference between the two processes lies in the step of peeling off a silicon film. The SOITEC process requires high temperature treatment for peeling off the silicon film, while the SiGen process allows the silicon film to be peeled off at ordinary temperature.
The SOITEC process, which requires high temperature for peeling off a silicon film, is susceptible to damage such as fracture and local cracking due to difference in thermal characteristics such as a thermal expansion coefficient when the handle substrate is made of a material different from silicon.
On the other hand, the SiGen process, which allows the silicon film to be peeled off at low temperature, is less susceptible to fracture and local cracking due to difference in thermal characteristics. However, this process is apt to allow the silicon film, which has been bonded to the handle substrate, to come off from the handle substrate at the bonded surface during the step of peeling, or apt to leave a trace of peeling or mechanically damage on the silicon film. That is because the silicon film is mechanically peeled off.
It has been known that damage due to the thermal or mechanical peeling becomes more significant toward the surface region (Ohmi, T. et al., “SOI No Kagaku”, published by Realize Science & Engineering Center Co., Ltd. in 2000, Chapter 2, Section 2, Paragraph 2).
It has also been known that sandblasting is used in the fogging (frosting) of SiO2-based substrates and parts made of glass, quartz and the like, sapphire-based substrates and parts, and the like. This is a method in which fine alumina or silica powder is sprayed onto a surface which is intended to be roughened, and widely used for various purposes.